The Universal Serial Bus (USB) standard was originally designed to support personal computer to telephone interconnect, ease of use and port expansion for a personal computer. Port expansion includes peripherals such as a mouse, keyboard, monitor, printer, scanner, modem, etc. Today however, electronic systems other than personal computers may also include a Universal Serial Bus to facilitate connections. Although most USB devices today are still peripheral devices, a motherboard or an equivalent, or an expansion card may in some cases include USB devices.
In order to enhance readability herein, a bus which is a Universal Serial Bus will also be referred to herein below as a USB bus in order to emphasize that the bus is being indicated, even though the term may be considered by some to be repetitive because the word “bus” is included in the acronym. Under the current USB standard, four wires are included in the USB bus: a power line (e.g. Vbus), a ground connection, and a pair of differential data leads (lines), denoted D+ and D− on which USB signals are transferred.